The present invention relates to the art of metal surface treatment. More specifically, the present invention relates to treatment of metal surfaces with a dilute solution of a poly-4-vinylphenol derivative or an acid salt of a poly-4-vinylphenol derivative. The treatment imparts improved corrosion resistance and paint adhesion characteristics to the metal surfaces.
The need for applying protective coatings to metal surfaces for improved corrosion resistance and paint adhesion characteristics is well known in the metal finishing and other metal arts. Traditionally, metal surfaces are treated with chemicals which form a metal phosphate and/or metal oxide conversion coating on the metal surface to improve the corrosion resistance and paint adhesion thereof. Also traditionally, the conversion coated metal surfaces have been rinsed or post-treated with a solution containing a hexavalent chromium compound for even greater corrosion resistance and paint adhesion.
Because of the toxic nature of hexavalent chromium compounds, expensive treatment equipment must be used to remove chromates from water effluent to prevent the pollution of rivers, streams, and drinking water sources. Hence, although the corrosion resistance and paint adhesion characteristics of conversion coated metal surfaces can be enhanced by an after-treatment solution containing a hexavalent chromium compound, in recent years there have been research and development efforts directed to discovering effective alternatives to the use of such post-treatment solutions. One alternative is provided in my earlier U.S. patent application, Ser. No. 210,910 now U.S. Pat. No. 4,376,000, for Composition for and Method of After-Treatment of Phosphatized Metal Surfaces filed on Nov. 28, 1980. The post-treatment compound of my earlier application is used in post-treatment solutions having an alkaline pH. It would, however, be desirable to have a post-treatment compound useful in post-treatment solutions over a broad pH range and, in particular, useful in an acidic post-treatment solution.
In accordance with the present invention a novel composition which is alternative to hexavalent chromium compound containing solutions is provided for use in acidic post-treatment solutions in a novel process for the post-treatment of phosphatized or conversion coated metal surfaces. Also, the present invention provides a solution and method for treating previously untreated metal surfaces including aluminum and zinc metal surfaces. The solution and method of the present invention are effective to enhance the corrosion resistance and paint adhesion characteristics of a conversion coated or uncoated metal surface. Further understanding of this invention will be had from the following disclosure wherein all parts and percentages are by weight unless otherwise indicated.